SPAN-CPT Installation | Chapter 2 |
2.2.1Mount the Antenna
For maximum positioning precision and accuracy, as well as to minimize the risk of damage, ensure the antenna is securely mounted on a stable structure that will not sway or topple. Where possible, select a location with a clear view of the sky to the horizon so each satellite above the horizon can be tracked without obstruction. The location should also be one that minimizes the effect of multipath interference. Ensure the antenna cannot move due to dynamics.
For a discussion on multipath, refer to An Introduction to GNSS on the NovAtel website.
2.2.2Mount the SPAN-CPT
Mount the SPAN-CPT in a fixed location where the distance from the SPAN-CPT to the GNSS antenna phase center is constant. Ensure the SPAN-CPT orientation, with respect to the vehicle and antenna, is also constant.
For attitude output to be meaningful, the SPAN-CPT should be mounted so the positive Z-axis marked on the SPAN-CPT enclosure points up and the Y-axis points forward through the front of the vehicle, in the direction the vehicle is moving.
Figure 4: SPAN-CPT Enclosure Mounting
Z
Y
X
Also, it is important to measure the distance from the SPAN-CPT to the antenna (the Antenna Lever Arm), on the first usage, on the axis defined on the SPAN-CPT enclosure. See also Appendix A, Technical Specifications on page 48 for dimensional drawings of the SPAN-CPT.
Ensure the SPAN-CPT and GNSS antenna cannot move due to dynamics and that the distance and relative direction between them is fixed.
The closer the antenna is to the SPAN-CPT, the more accurate the position solution. Also, your measurements when using the SETIMUTOANTOFFSET command must be as accurate as possible or at least more accurate than the GNSS positions being used. For example, a 10 cm error in recording the antenna offset results in at least a 10 cm error in the output.
Millimeter accuracy is preferred.
The offset from the SPAN-CPT to the antenna and/or a user point device, must remain constant especially for RTK or DGNSS data. Ensure the SPAN-CPT, antenna and user point device are bolted in one position perhaps by using a custom bracket.
